Secondary batteries, which can be charged and discharged, have been widely used as energy sources for wireless mobile devices. Also, secondary batteries have attracted considerable attention as power sources for devices which require high power output and large capacity, including electric vehicles (EV), hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (Plug-In HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Such devices use a middle or large-sized battery module having a plurality of battery cells electrically connected to each other to provide high power output and large capacity.
The middle or large-sized battery module is preferably manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (unit cell) of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is low, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
FIG. 1 is a perspective view typically illustrating a conventional pouch-shaped battery. A pouch-shaped battery 10 shown in FIG. 1 is configured to have a structure in which two electrode terminals 11 and 12 protrude from the upper and lower ends of a battery body 13, respectively, while the electrode terminals 11 and 12 are opposite to each other. A sheathing member 14 includes upper and lower sheathing parts. That is, the sheathing member 14 is a two-unit member. An electrode assembly (not shown) is received in a receiving part which is defined between the upper and lower sheathing parts of the sheathing member 14. Opposite sides 14a and upper and lower ends 14b and 14c, which are contact regions of the upper and lower sheathing parts of the sheathing member 14, are bonded to each other, whereby the pouch-shaped battery 10 is manufactured.
The sheathing member 14 is configured to have a laminate structure of a resin layer/a metal film layer/a resin layer. Consequently, it is possible to bond the opposite sides 14b and the upper and lower ends 14a and 14c of the upper and lower sheathing parts of the sheathing member 14, which are in contact with each other, to each other by applying heat and pressure to the opposite sides 14a and the upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14 so as to weld the resin layers thereof to each other. According to circumstances, the opposite sides 14a and the upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14 may be bonded to each other using a bonding agent. For the opposite sides 14a of the sheathing member 14, the same resin layers of the upper and lower sheathing parts of the sheathing member 14 are in direct contact with each other, whereby uniform sealing at the opposite sides 14a of the sheathing member 14 is accomplished by welding. For the upper end 14b and the lower end 14c of the sheathing member 14, on the other hand, the electrode terminals 11 and 12 protrude from the upper end 14b and the lower end 14c of the sheathing member 14, respectively. For this reason, the upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14 are thermally welded to each other, while a film type sealing member 16 is interposed between the electrode terminals 11 and 12 and the sheathing member 14, in consideration of the thickness of the electrode terminals 11 and 12 and the difference in material between the electrode terminals 11 and 12 and the sheathing member 14, so as to increase sealability of the sheathing member 14.
However, the mechanical strength of the sheathing member 14 is low. In order to manufacture a battery module having a stable structure, therefore, battery cells (unit cells) are generally mounted in a pack case, such as a cartridge. However, an apparatus or a vehicle, in which a middle or large-sized battery module is installed, has a limited installation space. For this reason, the space utilization is lowered if the size of the battery module is increased as the result of using the pack case, such as the cartridge. Also, the battery cells repeatedly expand and contract during the charge and discharge of the battery cells due to the low mechanical strength of the battery cells with the result that the thermally welded portions may be separated from each other.
In addition, the electrode terminals 11 and 12 of the pouch-shaped battery 10 have a larger area and a smaller thickness than the electrode terminals of the cylindrical battery or the prismatic battery with the result that electrical connection may be restricted during the configuration of the battery module or the battery pack.
Meanwhile, the battery module mounted in the middle or large-sized battery pack is generally manufactured by stacking a plurality of battery cells with high integration. Electrode terminals of the neighboring battery cells are electrically connected to each other.
FIG. 2 is a perspective view typically illustrating the electrical connection structure of a conventional battery module.
Referring to FIG. 2, a battery module 50 is configured to have a structure in which cell units 20 are connected in series to each other while the cell units 20 are stacked. In particular, every two battery cells 10 are connected in series to each other while an electrically insulative partition 15 is disposed between every two battery cells 10.
As a result, electrode terminals of the battery module are connected to each other by one to one welding at a single weld point.
When the cell units are connected in parallel to each other while being stacked, however, three or more connections between the electrode terminals are needed with the result that the structure of the battery module becomes complicated, and internal resistance increases when the same region is welded.
Consequently, there is a high necessity for a battery module that is capable of providing high power output and large capacity and minimizing internal resistance while maintaining welding reliability.